Frank Partnoy

When Standard & Poor's recently lowered the U.S. government debt rating for the first time in history, it set off a firestorm of criticism, from the Obama administration to Wall Street. The downgrade raised questions about the influence of S&P and other agencies, which also faced blame in the financial crisis of 2007-'08.

Years before the current economic crisis, former derivatives trader Frank Partnoy warned about the dangers of tricky financial trading. He joins Fresh Air to explain how we got where we are.